If engine idle rolls up and down, and diagnosis rules out Idle Air Control (IAC) valve issues and vacuum leaks, the Programmable Speedometer/Odometer Module (PSOM) can be at fault electronically. The instrument cluster will need to be replaced, the PSOM is inside the cluster.
Average mileage: 166,000 (116,000–216,000)
Engines affected: 4.2L V6, 5.0L V8, 5.8L V8
6 people reported this problem